Production of oil from oil shale through fractures



T T@ j "f-T T T* Y Nov. 8, A1966 PRODUCTION 0F OIL. FROM o IL sHALE THRUGH FRACTURES THOMAS 23,'284Q2s1 Filed Aug. 3 1. 1964 INVENTOR. R.w. THOMAS 3,234,281 v PRODUCTION or on.v FROM on. suALE THROUGH raacrunas Rosswell W. Thomas, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Aug. 3l, 1964, Ser. N0..393,1l3

8 Clan'. .(Cl. 16S-f2) The invention relates to the production of oil or fluid hydrocarbons from oil shale (shale containing kerogcn).

The productiozrof oil from oil shale by heating the shale by various means such as steam, down-hole combustion of a combustible gaseous mixture, an

electrical' resistance hcater,'an d injection of hot gases` other than stca'm has been attempted with little success. In situ combustion of shale 'has also been relatively unsuccessful because of the impervious andthe plastic nature ofthe shale. Fracturingof the shale prior to the application of heat thereto by in situ lcombustion or other means has been practiced with little success because the shale swells upon heating with consequent partial or complete closure of the fractures.

An early disclosure of fracturing oil shale and applying heat to the fractured shale i's found in Hoover et al., U.S. Patent 1,422,204, issued .luly l-, i922.

This invention is concerned with a novel method of producing fluid hydrocarbons from shale containing kerogen by application of heat thereto by in situ combustion or by other-means.

f After the shale hasbeen properly heated in an annular section extending substantially into the stratu'm, such as a foot or more, and substantial 'swelling has ensued, fracturing is effected in conventional manner utilizing any suitable trac'turing uid.-- Hot fluids such as air, CO2, N3 combustion gas, oii, steam', supcrheated water, or hot liquids, are the preferred fracturing means. .Fracturing is effected at a selected levelin the o il shale stratum,

After initial fraeturing the stratum is again heated, preferably, to the prescribed temperature so' as to effect cracking of the kerogen and further swelling of the stratum with extension-.of the swollen section deeper into the stratum along or beyond the fractures. The fractures are extended deeper into`the strat-um by applying fractur'ing pressure in the fractures adjacent the well, followed by further heating to extend the volume of shale within which kcrogen can eventually be heated above the cracking tempcrature and production of oil and/or gas thus achieved.-

Accordingly, an object of the-invention is to provide a novel process for producing uid hydrocarbons from the ke'rogen existing in au oil shale straturn.V A further Y object is to provide a novel process for utilizing a seq-uential'combinationof heating and fracturing in the produc tion of'oil from oilshale Other objects of the inventionv will become apparent upon consideration of the accompanying disclosure. i

A broad aspect of the invention comprises heating to an elevatcdtemperature a shale stratum containing kerogen around a well penetrating the stratum thereby causing l s'wellin" of theshale in asection adjacent the well, folj lowed by fracturing of the shale thru the swollensection and optionally pfopping the resulting fractures open, thereafter further heating the shale around the well and the fractures so as to crack the izerogen therein and release fluid hydrocarbons which .flow into the same well or another well thru the fractures, and recovering the hydrocarbon fluids fromnhe sameor an adjacent well. The initial l or subsequent heating of the shale is accomplished by any conventional means such asby injecting superheated steam so vthat the supcrhe'atcd steam passes ir: contact with the fracture system between the wells produces oil, gas, anda shale, burning a combustible gaseous mixture adjacent the t shale as in a down-hole heater, injectinga hot gas such as air or combustion gas, or use of an electrisal down-hole heater, or by combustion of some con-tained kerogen and/ or lits decomposition products- Shale swells and becomes more plastic as -it is heated and the contained kerogcn begins to crack at a temperature of about. 400 -F. in a steam-containing ambient (247 Fracturing :it more than one zone within the stratum and simultaneously heating the kerogen adjacent the fracture zones is within the scope. of the invention.` The fracturing fiuid(s) and the heating `iiuid(s) may or may not be the same. Part or all of the heating may be accomplished by combustion of the hydrocarbons already in the formation to be produced'.

Another embodiment of the invention comprises sequentially heating, swelling, fracturing, optionally. propping, and producing two or more spacedfapart wells in an oil shale strat'umand repea'ting the heating, swelling, frac,- turing, propping, and producingsteps in one lor more wells until flow paths, which remain open upon additional heating, have been established between two or more wells. These operations in the two or more wells may or may not be conducted simultaneously. The heating of the kerogen to the prescribed temperature cracks the kerogen and. A

leaves a carbon' residue. Heating the stratum along'the carbon residue, and extends the `ol-unie of shale to which access. may be had by heating r ieans, and/or for extending pressure-induced fractures. After establishment of sullicient permeability to permit continued ow of liuids,

hydrocarbon production can be effected by passing steam or other hot gas thru the fractures from one well to another, vor by igniting the stratum adjacent one of the wells to establish a combustion zone and moving the'combustion zone along the fractures and within the stratum to the other well. The combustion zone isestablished in conj'enticnal manner by heating the hydrocarbon material iu the stratum to ignition temperature and contacting the hot material with an Og-cont-ajning, combustion supporting field, such as air. After the combustion zone has been established, the same is moved thru the stratum by either direct or linverse drive. Using direct drive, the oxidant is injected thru the ignition well and combustion products and produced hydrocarbon fluids are recovered thru an other well. With inverse drive, the combustionsupporting gas is injected thru another well from which its passes thru the fractures to the combustion zone adjacent the ig nition well, thereby feeding the combustion zone and caus-A p.s.i.g. saturation prcssv'e of steam'land cracking is about 90% complete at about 700 FQ ln 'a dry ambient, the keroge-n in shale commences cracking at about 600 F.

and cracking of kerogen produces both gaseous and liquid hydrocarbons. The shale is heated to at least- 400 F. when heating in a steam ambient, as with steam injection and increases with increasing temperature. The` heating ing same to move toward the injection well.

A more complete understanding of the invention may be obtained by reference to the'a'ccompa'nying schematic drawing of which FIGURE/1 is a sectional elevation. thru a well penetrating 'an oil shale and FIGURE 2 is a similar view showing a pair of wells penetrating an oilv shale. The penetration may be partial orcomplete.

Referring to FIGURE l an oil shale 10 is penetra-ted by a well l12 which extends 'into stratum 14. Well 12 is provided with a easing 16 which extends to the top of stratum 10 and may extend thru this stratum if desired, in which case the casing i; perforated for fracturing and injection and withdrawal of fluids in known manner. A

tubing string 18le'xtends from well head 20 substantially to the bottom of the well forming an annulus 22 with' casing 1.6. When .down-hole heatingmcans is utilized in the process, a downihole heaterl 24 is' positioned on tubing string 18 or on aseparate suing of pip'e. Line 26 Q ;gfffiS-reellso thata combustion wave `is movedl thru the fractures and adjacent stratum 10 to well 38. In

"allv connects with tubing string 18 at or above the'wcll he:

for injection of heating and/ or fracturing tluid or for with; drawal of these fluids or of produced hydrocarbons` One or more packers may be used between tubing and and casing or formation. Line 28oonnccts with casing 15 4and annulus 22 for injection and/or withdrawal of fluids from the annulus. Fractures 30 are shown extending radially outwardlyffrom the well, representing one stage of the operation.

In operating with the arrangement shown in FIGURE l, heat is applied to stratum 10 adjacent the well by any suitable means as heretoforeset forth, as -by means of a down-hole heater 24, until a substantial annular section of shale around well 16, designated 32, has been elfective- 'ly heated and swollen. The swelling rma-y produce frac`- tures within the oil shale stratum outside of annular section 32 and/or in the overburden. `This fracturing aids 'in the production of' oil from the shale;

to extend the swollen shale area beyond section 32. After a substantial period of production in this manner, fractures 30 are enlarged in the area beyond section .32 and extended further into stratum 10 with or without propping agent injected into the extended fractures. This repettion of heating,fracturing,'optional propping, and production from well 16 is continued as `long as it is economic.

In performing the fracturing and optional propping` step, it may be advisable to utilize other wells which are suflciently close to well 12 to permit extending the fractures to the adjacent wells.

Referring to FIGURE 2, an oil stratum 10 overlying l an'underburden 14 is penetrated L" wells 36l and 38.

Well 36 has a casing 40 extending about to the up *r level of stratum 10 -and a tubing string 42'extendi'ng approximately to the bottom ofthe'well'. Well 38 is simi- -larly equippd with a casing 4'4,` a'nd a tubing string 45. Line 48 connects with casing 40 near the well'head and line 50 connectswith casing 44 in similar manner. These -lincs :provide for injection and withdrawal of fluids from the` well annuli. Lines 52 and 54 connect'with tubing strings 42 and 46, respectively, at or near the well heads for injection and withdrawal of tiuids. A fracture 51.3 tem designated 56 eventually is extended from well to well in stratum l0 and swollen area 58 is shown at th'at stag-3` of the process after fracturing and heating has been anv plied to the stratum between wells and passage of oir or other fluids between the wells is thereby made possible.

In the arrangement shown in FIGURE 2, both wells 36 and 38 are operated in the marmer described in con-Y nection with well 12 of FIGURE 1. Of course, it is to be understood that the successive iracturing and optional' propping steps are sequenced with the heating and production steps as heretofore described until suitable communication has been established for passage of uids between the wells. e

A heating tluid maythen 'ue `injected thru the fractures 56 from one well to another and produced fluids recov- "G-"LF-"fswellinga substantial section of shale adjacent the ered thru theother well. This heating duid may ooznprise 4superheated stearn, hot combustion gas, hot air, or any suitable means. In the event hot air is injected, for

example, thru well 36 a combustion zone is established situations nwhich hot air does not readily ignitethe kero gen and lfluid hydrocarbon in the stratum adjacent well 36, tubing string 42 may be withdrawn from within the stratum and ignition initiated by a charcoal pack soaked in heavy oil mich may be introduced to the well bore within stratum 10 and burned to establish a combustion zone in the adjacent stratum in accordance with conventional methods or by any suitable means. On the oombustion zone is established, the injection of'air thru well 36 is continued for a direct drive of the combustion front thru the stratum to well 3S or air is injected thruwell 38 andproduced fluids are recovered from well 36 thru tubing string 42. l

The propagation of a combustion .zone thruA the stratum between wells produces additional tluid hydrocarbons by cracking thelerogen in the adjacent stratum and this produces additional porous. coke which may be burned.4

on a second pass of. a combustion zone thru the stratum While FIGURE 2 shows only a pair of spaced-apart' wells, the process may be operated with any well pattern such as a 5, 7, or 9spot pattern or a pattern of parallel lines of wells, well 36 representing acentral well in a circular pattern in which a ring of wells 38 surround the central well or wells 36 and 33 may be representative of rows of parallel wells withothcr parallel rows adjacent these wells.

Certain modifications of the invention will become ap,- parent to those skilled in the art and the illustrative details disclosed are' not to be' construed as imposing unn'ec essary limitations on the invention.A

I claim:

l. The process for producing oil froinhoil shale containing kerogenwhich comprises the steps of:

(-1) heating said shale around a well-penetrating same tc an elevated temperature so as to swell a section of the shale around said well;

(2) fracturng the shale thru and beyond the .swollen section radially outwardly irom'said well; i (3) following step (2v), again heating the shale around said well so as to crack the i:erogen therein and cause .released hydrocarbon fluids to flow through said fracture into said well;

(4) recovering said hydrocarbon fluids from said well;

(5) continuing the heating of 'step (3) until the shale adjacent the area of the fracture remote from said well swells and closes the fractures in said area;

(6) following s tep (5), again .applying tiuid fracturing pressure on the shale around said well at fracture level so as to extend said fracture deeper into said shale; and

(7) repeating steps (4), (5), and (6).

2. The process of claim 1 wherein theheating in steps i (1) and (3) is effected by burning a combustible fuel-air mixture downhole in said welL 3. The process of claim 1 wherein the heating in steps (1) and (3) is effected by a downhole electric heater.

4. The process of claim 1 wherein the heating in steps (l) and (3) is effected by injecting-steam at a tempera 'ture 'of atleast 400 F. thru'rheA well into contact with the kerogen-contahting formation.

5. The process of claim 1 including the step cf injecting a propping 'agent into the fractures after each yf racturing step.

6. A process for producing oil from oil shalt: containing kerogen and penetrated by a pair of wells which comprises the steps of:

(1) heating said shale around each of said Wells at least to the swelling temperature of said shale thereby wells; (2) fractun'ng the shale thru and beyond the swollen section radially away from each well at substantially the same bedding plane;

(3) following step (2), .again heating the shale around each well so as to crack .s ,aid kerogen, causing' result- A ing tluid hydrocarbons to ow thru the fractures into said wells, and extending the swollen section deeper into the shale; (4) following step (3) again applying uidfmcturing .pressureto the shale in each well at the level of the existing fractures s o as to extend the fractures substantially beyond the expanded swollen section;

(5) following step (4), again heating thc shale around step (6) so to produce additional uid hydro-V carbons from the intervening shale; and

duced by the foregoing steps.

` (8) recoslering uid hydrocarbons from sid wells pro- I 'i he process of claim` 6 including the step of positioning a propping agent into the fractures with each frat:` turing Step.

8. The' process of claim 6 including the steps of:

(9) ignitng the shale adjacent the fracture at one well to establish a combustion zone;

(10) moving said combustion zone thru Said shale ad` n jacent said fracture toward the other wellby feeding air thereto so Aas to produce additional uid hydro. carbons; and (ll) recovering said additional hydrocarbons from atA least one of said wells.

References Cited by the Ezaniiner I UNITED STATES PATENTS 2,876,838 3/1959 l ililliat'rls 166-11 2,880,802O y 4/1959 Carpenter 166--11 2,952,450 4/1960 YPurre 1664-11 X 3,105,545 10/1963 Prats et al 166-39 3,137,347 6./1964 Parker 166-39 JACOB L NACKENOFF, Primary Examiner. CHARLES E. lOCONIELI., Examiner. i S. J. I VQVOSAD,h Assistant Exnmner. 

1. THE PROCESS FOR PRODUCING OIL FROM OIL SHALE CONTAINING KEROGEN WHICH COMPRISES THE STEPS OF: (1) HEATING SAID SHALE AROUND A WELL-PENETRATING SAME TO AN ELEVATED TEMPERATURE SO AS TO SWELL A SECTION OF THE SHALE AROUND SAID WELL; (2) FRACTURING THE SHALE THRU AND BEYOND THE SWOLLEN SECTION RADIALLY OUTWARDLY FROM SAID WELL; (3) FOLLOWING STEP (2), AGAIN HEATING THE SHALE AROUND SAID WELL SO AS TO CRACK THE KEROGEN THEREIN AND CAUSE RELEASED HYDROCARBON FLUIDS TO FLOW THROUGH SAID FRACTURE INTO SAID WELL; (4) RECOVERING SAID HYDROCARBON FLUIDS FROM SAID WELL; (5) CONTINUING THE HEATING OF STEP (3) UNTIL THE SHALE ADJACENT THE AREA OF THE FRACTURE REMOTE FROM SAID WELL SWELLS AND CLOSES THE FRACTURES IN SAID AREA; (6) FOLLOWING STEP (5), AGAIN APPLYING FLUID FRACTURING PRESSURE ON THE SHALE AROUND SAID WELL AT FRACTURE LEVEL SO AS TO EXTEND SAID FRACTURE DEEPER INTO SAID SHALE; AND (7) REPEATING STEPS (4), (5), AND (6). 